How to find SBR

Discussion in 'Exposure Discussion' started by kbrede, Jan 30, 2013.

  1. kbrede

    kbrede Member

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    I've been reading and I'm finding conflicting methods of calculating the SBR of a scene.

    One source says if your highlight is EV 14 and your shadow is EV 9, the SBR would be 5. So in other words just subtract.

    Another place I read that you don't subtract, but count each EV step. So in this example 9,10,11,12,13,14, which would give a SRB of 6. Or you could subtract and add one.

    So which one is right?

    Thanks,
     
  2. Dan Henderson

    Dan Henderson Member

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    To my mind it doesn't make any difference as long as you are consistent and YOU understand YOUR results. My mind processes things more naturally if I use your first example (highlights are 14, shadows 9 = SBR 5) because that is the way I process numbers in every other instance (something costs $7, I give the clerk $10, I anticipate $3 in change.)

    So in my workflow, I place my shadows on Zone III; if the highlights fall in in Zone VII my SBR is 4 and I give normal development. If highlights fall in Zone VIII SBR=5 and I give N-1; Zone VI I give N+1, etc.
     
  3. doughowk

    doughowk Subscriber

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    The key word in the term is "range". If you have an EV of 10 for shadow and 15 for highlight, the range of subject brightness would be from 10 to 15 inclusive, ie SBR = 6.
    From a quick search for the term, check here
    But as Dan said above, what's important is being consistent with your counting method.
     
    Last edited by a moderator: Jan 31, 2013
  4. markbarendt

    markbarendt Subscriber

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    The difference from "your normal" is what's important more than how you count.

    I use an incident meter. I measure once with dome pointed at the light source as my baseline. In a cross-lit situation I then point the dome at the camera and take a reading.

    The difference between those two readings in late afternoon is normally about 1-stop. I consider that a normal SBR.

    If the subject is backlit, the difference between baseline and dome at the camera readings might be 3-stops. High contrast, large/wide/high SBR.

    If the subject is front lit the difference is 0, so one stop less than my normal which indicates a small/narrow/low SBR.
     
  5. Stephen Benskin

    Stephen Benskin Member

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    1 to 2 is one a one stop range. EV 9 to 14 is 5 stops. BTW "Luminance" is the current term - log Subject Luminance Range (LSLR). Brightness is considered to be psychological while Luminance is psychophysical.
     
  6. kbrede

    kbrede Member

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    OK, nothing can ever be strait forward can it? LOL

    I'm trying to figure out how to measure a contrast range to find N, N+1, N-1. My idea was to use an incident reading to make the exposure, then switch to spot/EV to measure the spread of lights and darks.

    From what I've read the spread should be about 5 stops, zone III to zone VII, for normal. If the spread is zone III to zone VIII, that would be N-1.

    So taking that into consideration would the LSLR for my original example (EV14 and EV 9) be an LSLR of 5 or 6? In other words, "N" or N-1?"

    Thanks,
     
  7. kbrede

    kbrede Member

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    I think I mentioned this before Mark, but I wish you'd write an incident meter howto. There's tons of stuff out there for spot metering but incident not so much. All I've read about is duplexing and pointing the incident meter at the camera. Is it really that simple?
     
  8. markbarendt

    markbarendt Subscriber

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    Yes. Take it out of the box, put in the battery, set the ISO to box speed, set the aperture or time you prefer, extend the dome, point it at the camera, take the reading, use the setting it tells you to. If you just do that when using any negative film you will get good usable negatives almost without fail.

    Sure there are some nuances to learn, ways to use them in non-standard situations, ways to be even more accurate, and there other tweaks you can add, but even without the advanced class stuff incident metering is truly simple and incredibly reliable.

    BTW the method I described above is essentially how BTZS finds SBR, they just add a specific number to the result (5 or 6 ????) to translate it into a number that most zone system people understand.

    (And o.k. I'll think about writing an article here. No promises on when though.)
     
  9. Stephen Benskin

    Stephen Benskin Member

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    The statistically average scene is 7 1/3 stops. The Zone III to Zone VIII range is for shadows with good detail and an average highlight (non specular). If you want to place EV 9 on Zone III and EV 14 falls on Zone VIII, that would be considered N.
     
  10. cowanw

    cowanw Member

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    Between 9 and 14 there are 5 spaces (or zones or changes in luminance or what ever you want to call them) just as the number of inches between 9 inches and 14 inches is 5 inches. The EV number represents all the ev shades between it and the next number.
     
  11. cowanw

    cowanw Member

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    Each EV represents all the shades between it and the next highest number. 9 represents all the shades between 9 and 10. 14 represents all the shades between 14 and 15. There are 6 such divisions of shade.
     
  12. Usagi

    Usagi Member

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    I have learn that SBR is highlight reading - shadow reading + 5. Thus shadow reading 9 and highlight reading 14 would be SBR 10.

    The incident meter value is average of apr. 5 stop range. So shadow value extends 2.5 stops towards dark from reading and highlight includes values up to 2.5 stop above reading.
     
  13. baachitraka

    baachitraka Subscriber

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    True, when BTZS is employed.